1. Technical Field
The present invention relates to a sheet folding apparatus, a sheet post-processing apparatus and an image forming apparatus, which perform a folding process of a sheet.
2. Description of Related Art
A sheet folding apparatus for folding a sheet into the shape of half-fold, which folds a sheet at a center line, and of three-fold, is widely used as a sheet post-processing apparatus of an image forming apparatus, such as an electrophotography image forming apparatus.
For example, Unexamined Japanese Patent Application Publication No. 2004-99199 (JPA2004-99199) discloses a sheet folding apparatus, which performs half-fold or three-fold using a plurality of rollers.
In the sheet folding apparatus disclosed in JPA2004-99199, the first folding process of a paper sheet is performed by nipping the paper sheet and conveying the paper sheet with a pair of rollers in the upstream side, and the second folding process of a sheet is preformed by nipping the paper sheet and conveying the paper sheet with a pair of rollers in the downstream side.
The sheet folding apparatus disclosed in JPA2004-99199 can perform half-fold or three-fold of a sheet.
In the sheet folding apparatus disclosed in JPA2004-99199, the first folding process is performed by inserting a sheet between a pair of rollers in the upstream side by using a folding plate.
And the sheet is inserted between a pair of rollers in the downstream by butting the sheet against an edge stop member and making the sheet crooked by the conveyance of the pair of rollers in the upstream side, and the second folding process is performed by this sheet insertion.
FIG. 1 schematically illustrates the sheet folding apparatus disclosed in JPA2004-99199.
As illustrated in FIG. 1, a paper sheet S is nipped and conveyed by a pair of rollers R1 and R2 in the upstream side, and the edge of the sheet butts against the edge stop member T. Then, the paper sheet S stops.
When rollers R1 and R2 rotate further and convey the paper sheet S, the paper sheet S is crooked in the middle toward the side of the pair of rollers R2 and R3 in the downstream side.
The edge of a crooked section of the paper sheet S advances into the nip between rollers R2 and R3.
When the rollers R2 and R3 rotate, the folding process of the paper sheet S is preformed while being conveyed by the rollers R2 and R3.
The guiding member G between the rollers R1 and R2 and the edge stop member T forms a crooked conveyance path so that the paper sheet S is made crooked toward the rollers R2 and R3 side.
However, the paper sheet S may be crooked in the opposite side, which departs from rollers R2 and R3 side but not toward the roller R2 and R3, by the conveyance of the rollers R1 and R2 depending on the state of the paper sheet S.
Irregular crookedness of such a paper sheet S is generated in the case where the paper sheet S is curled.
When irregular crookedness of such a paper sheet S takes place, malfunctions, in which caused is poor conveyance, such as jam, and poor folding with a bent fold line or a slanting fold line, will occurs.
In order to avoid this, it may be feasible to form the structure of the guiding member G so that the paper sheet S is made crooked strongly. But, when it does so, smooth conveyance of sheet S will be impeded and it will become easy to generate poor conveyance, such as jam.
In the sheet folding apparatus illustrated in FIG. 1, since the space in which a paper sheet can move freely between the nip of rollers R1 and R2 and the upstream side edge of the guiding member G is formed and control of the paper sheet S in this space is difficult too be performed, the problem (i.e., poor conveyance) mentioned above and a poor folding process may occur.